This is a very US centric view. In virtually all of Europe, for instance, WhatsApp is the go to messenger and no one uses SMS anymore.
In some countries - primarily Russia, but also in Europe e.g. Germany and increasingly the UK - Telegram is also popular, and Viber is popular in African countries, while WeChat is used extensively in China, and so on... people have to use the messenger everyone else is on.
I do use Signal to chat to close friends, and Telegram has become popular enough as a second to WhatsApp that I often use it too, but as others have said it's a strong network effect.
The only other messenger I can remember having the position WhatsApp has was BBM back in the day. But as soon as BlackBerries went out of fashion it was all WhatsApp and has been ever since.
In some countries - primarily Russia, but also in Europe e.g. Germany and increasingly the UK - Telegram is also popular, and Viber is popular in African countries, while WeChat is used extensively in China, and so on... people have to use the messenger everyone else is on.
I do use Signal to chat to close friends, and Telegram has become popular enough as a second to WhatsApp that I often use it too, but as others have said it's a strong network effect.
The only other messenger I can remember having the position WhatsApp has was BBM back in the day. But as soon as BlackBerries went out of fashion it was all WhatsApp and has been ever since.